Regarding a method for increasing the capacity of transmission on the data transmission channel for transmitting data, the number of links (namely, number of bits) for transmitting data has been increased and a parallel synchronization data transmission method has been employed, which can increase the capacity of transmission. In the parallel synchronous data transmission method, however, it is required that the timing of each link coincides in units of bits when data arrives at the receiving side. However, as the transmission distance increases, a difference in the transmission distance is created between links to cause to generate a transmission delay and to bring about a difference of arrival time (skew) between links. In order to perform a long-distance data transmission using the parallel synchronization data transmission method, the problem of the skew has to be solved. Therefore, the conventional parallel synchronization data transmission method was not suitable for the long-distance data transmission.
On the other hand, there is a serial data transmission method using a technique, in which a parallel signal is time-multiplexed to be serialized, and after being transmitted as a serial signal, being subjected to parallel-conversion again at the receiving side (generally referred to as “SerDes” (Serializer/De-serializer)). By using the SerDes, the problem of the skew between bits can be solved. This becomes remarkable when the above-mentioned parallel data transmission is accelerated, so that the long-distance data transmission becomes possible.
With the increase of IP traffic in recent years, as higher speed is also required in the field of transmission, the capacity of a transmission of more than 100 Gbps becomes necessary. However, in order to have a further broader bandwidth in the serial data transmission method, it is necessary to increase the density along the time direction by reducing the pulse width of one bit, since there is a physical limit, it was not possible to increase the bandwidth very much. This is why using both a parallel processing technique and a high-speed technique for serial signal is important.
Then, in order to transmit high-speed serial data by further performing a parallel-conversion, it is necessary to solve the skew, which became a problem in the parallel synchronization data transmission method. However, if it is assumed that each serial signal becomes a high-speed signal of 10 Gbps, the pulse width of one bit becomes 100 ps and it is eventually impossible to transmit it by synchronizing in units of bits. Therefore, a method is considered in which a serial signal is divided into blocks having a certain width to perform a synchronization transmission in units of blocks. Non-patent document 1 discloses (IEEE Std 802.3ae-2002 Edition, “Media Access Control (MAC) Parameters, Physical Layers, and Management Parameters for 10 Gb/s Operation”) in the XAUI (10 Gigabit Attachment Unit Interface), a method is employed, which utilizes an 8B/10B encoding method, performing a correction of the skew in units of this code.
On the other hand, in order to perform a long-distance data transmission by a parallel-conversion of a high-speed serial signal, it is possible to utilize a WDM (Wavelength Division Muitiplex) transmission method to transmit data by allocating each serial signal to a different wavelength. However, the WDM has a problem in which a cross talk with an adjacent wavelength becomes large, so that the error rate (BER: Bit Error Rate) of the line becomes large in order to lower the bandwidth. When the distance is comparatively short, it is possible to perform a parallel transmission by each fiber by bundling a plurality of fiber and using a ribbon fiber, however, since an optical fiber for use is a MMF (Multi-Mode Fiber), a long-distance transmission causes a large signal degradation to increase the BER. Further, since in the optical transmission, a plurality of laser oscillators and receivers are mounted on a one module, and at the same time, there is a plurality of optical link paths (frequency of parallelism), a failure rate of the entire system at least increases the times of the frequency of parallelism, when compared with a single laser oscillator. Moreover, there is a problem that when any one of a plurality of lines comprising the channel fails, the line immediately breaks down.
Accordingly, in the patent document 1 (JP 11-32008 A), the optical transmitting equipment is disclosed, which transmits redundant bits for performing an error correction using another path in addition to a path for transmitting a data signal in order to improve the reliability of the transmission line and at the same time not to accelerate the transmission speed.
In the patent document 2 (JP 2002-118540 A), a method for an optical transmission is disclosed, in which information data is transmitted by using a plurality of channels, and at the same time, a check data for the information data is transmitted by using another channel, and on the receiving side, an error correction for each channel is conducted by the check data, and the check data can be transmitted and the error correction can be performed without increasing the transmission speed of the channel for transmitting the information data.